Down hole hydraulic pump

ABSTRACT

A down hole pump adapted to be driven by a power fluid circulated into the hole from the surface and including at least one main power piston, a working barrel surrounding the power pistons, a pair of power fluid charging ports in the working barrel, a pair of power fluid discharge ports in the working barrel, fluid passageways connecting the ports to the surface, and a double slide valve assembly positioned in the working barrel and cooperating with the power pistons during portions of the stroke thereof for alternately opening one of the charging ports and closing one of the discharge ports while concurrently closing the second charging port and opening the other discharge port, then, at a different time, reversing the status of the four ports. The slide valve assembly is actuated to open and close the ports at critical times by contact of at least one power piston with this assembly, coupled with the resilient bias of a spring and ball assembly cooperating with a cam surface on a portion of the slide valve assembly.

United States Patent m1 3,582,238

[72] Inventor Verbol J. Devine 2,645,208 7/1953 Hardesty l03/46X 2912 Epperly Drive, Oklahoma City, Okla. 3,276,381 l/l 966 Harklau et al. 103/5 lX 2 l 1 pp No 5 Primary ExaminerRobert M. Walker Filed p 1969 Attorney-Dunlap, Laney, Hessin and Dougherty Patented Junel,l97l

ABSTRACT: A down hole pump adapted to be driven by a power fluid circulated into the hole from the surface and ineluding at least one main power piston, a working barrel sur- [541 DOWN HOLE HYDRAULIC PUMP rounding the power pistons, a pair of power fluid charging 13 Claims 5 Drawing nag ports in the working barrel, a pair of power fluid discharge ports in the working barrel, fluid passageways connecting the U.S. P u t th f e nd a double slide valve assembly posi. 91/4] 1 tioned in the working barrel and cooperating with the power [5]] lnt.Cl ..F04b 17/00, pistons d i ti f the troke thereof for alternately F15b I opening one of the charging ports and closing one of the Field of Search 103/44, 45, discharge ports n concurrently dosing h Second h 51; 9l/344v 417/377; 397 ing port and opening the other discharge port, then, at a different time, reversing the status of the four ports. The slide [56] References Cited valve assembly is actuated to open and close the ports at criti- UMTED STATES PATENTS cal times by contact of at least one power piston with this as- 1,714,425 5/[929 Knab 103/5 1 X sembly, coupled with the resilient bias of a spring and b ll 2,057,364 WI 1936 Bystricky... l03/50X sembly cooperating with a cam surface on a portion of the 2,346,026 4/1944 Hendricks l03/46X slide valve assembly.

DOWN HOLE HYDRAULIC PUMP BACKGROUND OF THE INVENTION I. Field of the Invention This invention relates to down hole hydraulically actuated pumps, and particularly, to such pumps having slide valves functioning to open and close porting used to effect stroke reversal of such pumps.

2. Brief Description of the Prior Art Many types of both single-acting and double-acting down hole hydraulic pumps have been heretofore used for producing hydrocarbons from petroliferous subterranean formations. Pumps of this type generally involve some type of working barrel in which a working piston is driven in a reciprocating movement by a hydraulic power fluid delivered to the pump from the surface. In some instances, the hydraulic power fluid is maintained in an isolated system, both for circulation into the hole to the working barrel of the pump, and for return to the surface. In other arrangements, the hydraulic power fluid is mixed with the production fluid being produced from the subterranean formation prior to its return to the surface. In either eventuality, it is necessary to provide reliable valving of some type in the pump in order to transfer the flow of power fluid from one side of the power piston to the other side of the power piston in order to effect stroke reversal. The types of valving heretofore provided have worked on various principles, and have functioned with varying degrees of effectiveness. In some instances, the valving is susceptible to sticking or malfunction over extended periods of use, rendering the hydraulic pumps in which it is employed of marginal advantage over other types of pumps, such as sucker rod pumps or other types of hydraulically actuated pumps.

BRIEF DESCRIPTION OF THE PRESENT INVENTION The present invention provides a hydraulically actuated down hole pump which can be used over an extended period of time for producing oil from relatively deep subterranean formations. Broadly described, the hydraulically actuated down hole pump of this invention includes a working barrel which has reciprocably positioned therein, either a single power piston or a pair of power pistons which are interconnected to each other and which stroke together. Suitable piping or conduits are provided for delivering a hydraulic power fluid to the working barrel from the surface, and the working barrel is ported so as to receive and discharge the power fluid at different times during the stroke of the power pistons.

As is well understood in the art, it is necessary to provide multiple porting above and below each of the power pistons which are provided in the pump in order that during one directional reciprocation of each of such power pistons, power fluid may be delivered to one side of one or both the power pistons from the surface, and discharged to the surface from the other side of the power pistons toward which the pistons are moving. It then follows that in order for the conduits conveying power fluid to and from the working barrel to be used interchangeably, dependent upon the particular portion of the stroke cycle in which the piston is moving, suitable valving must be utilized for redirecting the flow of the power fluid.

In the present invention, the valving employed in the down hole hydraulic pump takes the form of a pair of interconnected slide valves which are concurrently actuated by dual forces provided, in the first instance, by contact of a portion of the valve assembly with one of the main power pistons and, in the second instance, by a carry-through snap action imparted to the valve assembly by a spring-biased camming mechanism. The spring-biased camming mechanism assures that the slide valve assembly will be positively moved in the proper sequence to the desired positions in which the working barrel is ported for causing the power pistons to reciprocate in the desired directions to deliver the necessary pumping action.

From the foregoing broad description of the invention, it will be perceived that it is an object of the present invention to provide an improved down hole hydraulically actuated pump.

LII

Another object of the invention is to provide a down hole hydraulically driven pump which has a pair of positively actuated slide valves which are characterized in having a long and trouble-free service life.

Additional objects and advantages of the invention willbecome apparent as the following detailed description of the invention is read in conjunction with the accompanying drawings which illustrate the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a partially sectional and partially elevational view of a double-acting, hydraulically actuated down hole pump constructed in accordance with the present invention.

FIG. 2 is a sectional view taken along line 22 of FIG. 1.

FIG. 3 is a sectional view taken along 3-3 of FIG. 1.

FIG. 4 is a partially sectional, partially elevational view ofa. single-acting, hydraulically actuated down hole pump constructed in accordance with the invention.

FIG. 5 is a sectional view taken along 55 of FIG. 4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION Referring now to the drawings, and initially to FIG. I, shown therein is a down hole hydraulic pump constructed in accordance with the invention. The embodiment of the invention illustrated in FIGS. 1 3 is a double-acting pump and includes a working barrel 10 in which are located an upper power piston 12 and a lower power piston 14. The power pistons 12 and 14 are interconnected by an elongated connecting rod 16 which extends between the pistons and centrally in the pump barrel 10. The connecting rod 16 passes through a central-divider block 18 positioned intermediate the ends of the working barrel 12.

The divider block 18- sealingly engages the internal walls of the working barrel l0, and is retained in position by means of suitable screws 19 extended through the working barrel into the divider block 18. As will be noted in referring to FIGS. 1 and 3, the divider block I8 has a portion cut away from one side thereof to accommodate a cam block 20 in the recess 21 thus formedin the divider block 18. The connector elements 22 and 24 are secured at their opposite ends to slide valve members 26 and 28, and with the slide valve members, for a portion of a slide valve assembly designated generally by reference numeral 30. The slide valve members 26 and 28- each constitute annular sleeves which slidingly engage the internal walls of the working barrel 10' for sliding movement therealong. Connection of each of the connector members 22 and 24 to the slide valves 26 and 28 is through a spider 32 secured inside each of the slide valves in the manner best illustrated in FIG. 2. Each spider 32 also slidingly accommodates the push rod 16 through a bore formed axially therethrough.

Resting upon the-central divider block l 8'and extending upwardly around the elongated connecting rod 16 is a helical spring 34. The upper end of the helical spring 34 bears against the underside of the spider 32 and is a fairly weak spring which is merely sufficient to oppose and balance the weight of the slide valve assembly 30'. Secured to the working barrel 10 at a location which is opposite the recess 21 in the cam block 20 is a first spring and ball assembly, designated generally by reference numeral 36.

The first spring and ball assembly 36 includes a cap plate 38,, which is secured by screws 40 or other suitable means over an aperture formed in the side of the working barrel 10. The cap plate 38 is recessed at its central portion, with the recess therein aligned with the aperture in the working barrel 10. A

spring 42 is seated in the recess in the cap plate 38 and bears against a ball 44 and forces such ball 44 against the cam block 20. As will appear in referring to FIG. 1, the cam block 20 has a pair of adjacent semispherical recesses formed in the outer surface thereof, and the ball 44 is biased by the spring 42 into one of these recesses. As the cam block 20 is shifted by the shifting of the slide valve assembly 36 as hereinafter described, the ball 44 moves from one of the recesses in the cam block to the other, and in doing so, biases the slide valve assembly upwardly or downwardly within the working barrel with a snap action to assure positive seating of the slide valve members 26 and 28 as more specifically hereinafter described.

Mounted on the working barrel at locations opposite the slide valve rnember 26 and the slide valve member 28 are second and third spring and ball assemblies, 46 and 48, respectively. Each of these assemblies is constructed substantiully identically to the spring and ball assembly 36, and is aligned with an aperture or recess formed in the working barrel. In the case of the second spring and ball assembly 46, the ball 44 thereof projects into contact with a portion of the slide valve member 26 which carries a cam depression, and the ball moves alternately into and out of this cam depression to further aid in producing the snap action which moves the slide valve assembly from one operative position to another. The third spring and ball assembly 48 functions substantially the same as the spring and ball assembly 46. It should be pointed A out that, in some instances, the spring and ball assembly 36 may aione provide the snap action which is desired, and the spring and ball assemblies 46 and 48 can be eliminated from the pump structure. in other cases, economy of manufacture is effected and satisfactory performance is obtained by including in the structure only the spring and ball assemblies 46 and 48, with the concurrent elimination of the spring and ball assembly 36.

Projecting downwardly from the lower side of the upper power piston 12 are a pair of resilient metal fingers 52 which function to contact rods 54 projecting upwardly from the spider 32 in the slide valve member 26. Similarly, a pair of spring metal fingers 56 extend upwardly from the upper side of the lower power piston 14 and are positioned for contacting the rods 58 which project downwardly from the spider 32 secured in the lower slide vaive member 28.

For the purpose of conveying power fluid from the surface to the down hole hydraulic pump, a hydrauiic power fluid charging conduit or passageway 60 is provided. The passageway 60 has a first branch 60a which is connected through a suitable fitting c-r port to the interior of the working barrel 10 at the location which is below the central divider block 18. A second branch 60b of the conduit 60 is connected through a suitable port to the interior of the working barrel 10 at a location which is above the central divider block i8.

For the purpose of permitting power fluid to be exhausted from the pump, a power fluid discharge conduit 62 is provided which includes a branch 62a which communicates with the interior of the working barrel 10 at a location between the upper side of the central divider block. 18 and the location at which the branch conduit 60b of the power fluid charging conduit 60 enters the working barrel. A second branch 62b of the power fluid discharge conduit 62 enters the working barrel 10 through a fitting or port which is located between the point of connection of the branch 60a of the conduit 60 to the working barrel and the lower side of the central divider block 18.

Extending from the lower end of the working barrel 10 is a standing valve housing 66 which includes a movement limiting cage 68 and a standing valve ball 70. The standing valve ball 70 seats upon a seat formed on the upper end of a tubing 72 which has a perforated sandpipe 74 secured to the lower end thereof. A production fluid discharge conduit 76 extends from a lower end of the working barrel 10 and contains a check valve 77 which prevents retrograde flow of production fluid from this conduit back into the working barrel 10. The upper end of the-production fluid discharge conduit 76 is connected to a fluid return conduit 78 which communicates with a standing valve housing 80 formed on the upper end of the working barrel 10. The standing valve housing 80 contains a cage 82 and a standing valve ball 84 which is shown resting upon a seat formed at the upper end of an opening 88 formed through the closed upper end of the working barrel 1G.

Communicating with the interior of the upper end of the working barrel 10 through the closed upper end of the working barrel is a production fluid conduit 90 which contains a check valve 92 preventing retrograde flow of production fluid from the interior of the working barrel l0 downwardly through the production fluid conduit to a sandpipe 94 located on the lower end thereof. lt will be understood that the sandpipes 74 and 94 secured to the lower ends of the conduits 76 and 90, respectively, are disposed in the lower end of the well bore, and are adapted to receive production fluid from the producing formation. It will also be noted that the upper end of the conduit 62, after passing through a check valve 96, is also connected to the fluid return conduit 78 and charges power fluid thereto after such power fluid is exhausted or discharged from the working barrel 10.

Operation of the Embodiment Illustrated in FIG. 1

In the use of the down hole hydraulic pump illustrated in P16. 1, hydraulic power fluid is charged to the pump from the surface through the conduit 60. Hydraulic power fluid can enter the working barrel i0 through either the branch 600 or the branch 60b, depending upon the status of the slide valve members 26 and 28 at that time. In the status illustrated in FIG. 1 of the drawings, the branch 60a of the conduit 60 cannot charge hydraulic power fluid to the interior of the working barrel 10 because it is closed by the slide valve member 28. Hydraulic power fluid can, however, be charged to the interior of the working barrel 10 above the central divider block 18 since, in the illustrated status of the pump, the upper slide valve member 26 does not extend across and close the branch conduit 60b. Thus, at this time, hydraulic power fluid is troduced to the interior of the working barrel 10 at a location above the central divider block 18, and the upper power piston 12 is driven upwardly within the working barrel 10.

As the upper power piston 12 moves upwardly in the work ing barrei 10, it carries with it'the lower power piston 14 as a result of the interconnection formed by the elongated connecting rod 16. With the movement of both the upper power piston 12 and the iower power piston 14 upwardly within the working barrel 1!), any liquid which may be located above the upper power piston 12 is forced upwardly through the standing valve housing and into the fluid return conduit 78. This liquid is returned to the surface through this conduit. The liquid forced out of the top of the working barrel 10 by upward movement of the power piston 12 is prevented from flowing downwardly through the conduits 76 and by the check. valves 77 and 92, respectively, located in these conduits.

At the time that the upper power piston is forcing any liquid thereabove upwardly through the standing valve housing 80 and into the fluid return conduit 78, the upward movement of the lower piston 14 forces the hydraulic power fluid which has been previously introduced above this piston out through the branch 62b of the conduit 62, through the check valve 96 and into the Fluid return conduit78. Thus, the fluid passed upwardly to the surface via the conduit 78 is any fluid located above the upper power piston 12 (which, as will be hereinafter explained, is production fluid) and the exhausted hydraulic power fluid which enters the conduit 78 from the conduit 62.

Upward movement of the lower power piston 14 also effectively draws production fluid upwardly through the standing valve housing 66 from the sandpipe 74 which the production fluid enters from the surrounding subterranean formation. The reduced pressure created in the lower end of the working barrel 10, coupled with the movement of the production fluid upwardly into the standing valve housing 66, effectively lifts the standing valve 70 off of its seat and permits the upward flow of production fluid into the working barrel to occur. Thus, the space between the lower power piston 14 and the lower end of the working barrel 10 is filled with this production fluid during the upstroke of the lower power piston 14. When the power pistons 12 and 14 reach the upper end of their strokes, the spring fingers 56 on the upper side of the lower power piston 34 will strike the rods 58 projecting down from the spider 32 mounted in the lower slide valve member 28.

As a result of this contact, which is cushioned by the springs 56, the slide valve assembly 30 will be shifted upwardly. The shifting of the slide valve assembly 30 results in an upward shifting or movement of the slide valve member 26 and the slide valve member 28 so that the branch conduit 60b becomes covered by the upper slide valve member 26, and the branch conduit 62b simultaneously becomes covered or closed by the lower slide valve member 28. Simultaneously, the branch conduit 60a of the hydraulic power fluid conduit 60 is opened by upward movement of the lower slide valve member 28, and the branch conduit 62a is opened by upward movement of the upper slide valve member 26. it is important to point out here that after the initial upward increment of movement of the slide valve assembly 30 has been commenced as a result of contact of spring fingers 56 with the rods 58, the completion of the shifting of the slide valve assembly is effected by the snap action developed by the spring and ball assemblies 36, 46 and 48. These assemblies function so that the contact of the spring fingers 56 with the rods 58 move the slide valve assembly, and specifically, the upper slide valve member 26, the lower slide valve member 28 and the cam block 20, upwardly with respect to the balls 44. The balls thus move onto the high spot adjacent depressions on the several cam surfaces,'and then the balls snap into the depressions under the resilient bias of their respective springs 42. Thissnap action drives the slide valve assembly 30 to the completion of its upward shifting movement, and thus positively seats the upper and lower slide valve members 26 and 28, respectively, at the locations in which they cover the branch conduits 60b and 6212 respectively.

After the slide valve assembly 30 has been shifted in the manner described, the branch conduit 60a of the hydraulic power fluid charging conduit 60 has been placed in communication with the interior of the working barrel at a location above the lower power piston 14. Thus, hydraulic power fluid. can flow into the working barrel 10 and act against the upper side of the lower power piston 14. At the same time, the introduction of power fluid to the upper end of the working barrel 10 from the branch conduit 60b has been terminated by the closing of this branch conduit by the slide valve member 26. Thus, power fluid ceases to push upwardly against the lower side of the upper power piston 12. Under these conditions, the power pistons 12 and 14 commence to move downwardly in the working barrel 10. As the lower power piston 14 moves downwardly in the working barrel 10, the production fluid which has been previously drawn upwardly into the lower portion of the working barrel through the standing valve housing 66 is forced outwardly into the production fluid discharge conduit 76' as the standing valve 70 is forced downwardly against its seat located at the upper end of the conduit 72. The seating of the standing valve 70 prevents any of the production fluid from flowing back through the conduit 72 and through the sandpipe 74. The production fluid forced into the conduit 76 passes through the check valve 77 and into the conduit 78 to which the production fluid conduit 76 is connected at its upper end.

As the upper power piston 12 moves downwardly in the working barrel 10, production fluid is drawn through the sandpipe 94 and into conduit 90 due to the reduced pressure created in the upper end of the working barrel above the upper power piston 12. This production fluid flows through the check valve 92 and into the space above the power piston 12 so as to at'least partially fill this space.

Downward movement of the power pistons 12 and 14 continues until the spring fingers 52 contact the upper ends of the rods 54 securedto the upper side of the spider 32 which is located in the upper slide valve member 26. At this time, the first commencement of the snap action of the slide valve assembly is commenced, with the slide valve assembly being moved downwardly in the working barrel 10. The snap action is carried through by the spring and ball assemblies 36, 46 and 48 heretofore described, so that the status of the branch conduits 60a, 60b, 62a and,62b is reversed. The reversal of the status (that is, whether they are open or closed) of these branches of the conduits 60 and 62 effects a stroke reversal of the power pistons 26 and 28 in the manner hereinbefore described. in this manner, the cycle of the pump is completed.

A single-acting embodiment of the down hole hydraulic pump of the invention is depicted in FIGS. 4 and 5. As shown in these FIGS, the pump includes an outer tubing 100, an inner tubing 102 and a working barrel 104 which is connected to the lower end of the inner tubing 102. The working barrel 104 may be of substantially uniform diameter over its length, or it may, as in the illustrated embodiment, include an en larged diameter portion 104a which is secured to the lower end of a relatively smaller diameter portion [041). A fluidtight partition 106 extends transversely across the working barrel 104 at the intersection of the relatively larger diameter portion 1040 with the relatively smaller diameter portion 10%. Slidingly disposed in the relatively. larger diameter portion 104a of the working barrel 104 is a power piston 108. The power piston 108 is provided with suitable sealing rings 110 and 112 around its outer periphery to sealingly engage the internal walls of the large diameter portion 104a of the working barrel 104. Secured to the bottom side of the power piston 108 is an elongated tubular member 114 which carries a pump piston 116 at its lower end. Pump piston 116 carries-a sealing ring 118 around its outer periphery for sealing engagement with the internal wall of a pump barrel 120 which is secured to, and communicates with, the lower end of the working barrel 104. The pump piston 116 contains a valve seat 122 upon which is seated, during one portion of the operatingstroke of the pump, a traveling ball valve 124. The traveling ball valve 124 can move upwardly a limited distance within the tubular member 114 until it strikes an upper seat 126 which has an orifice 128 therethrough which is closed upon seating of the ball valve 124 in the manner depicted in FIG. 4. Between the seat 126 and the seat 122 are a plurality of radial orifices 130 formed in the side of the tubular member 114.

Projecting downwardly into the relatively large diameter lower portion 104a of the working barrel 104 is the lower end portion of an actuator rod 132. The actuator rod 132 has an upper collar 134 and a lower collar 136 spaced axially therealong and secured to the actuator rod for movement therewith. The power piston 108 slidingly surrounds the actuator rod 132 at a location between the upper collar 134 and the lower collar 136.

It will be noted that the actuator rod 132 extends through a bore 140 formed through the center of the power piston 108 and that fluid leakage along the actuator rod 132 through this bore is prevented by an annular sealing element 142 disposed around the rod 132 and within the bore 140. The actuator rod 132 extends upwardly and centrally within the relatively small spider and is likewise secured by a suitable spider 152 to the lower end of the upper slide valve member 148.

Between the lower slide valve member 146 and the upper slide valve member 148, the actuator rod 132 extends through a central bore 154 which is centrally formed in a central di-.

vider block 156 secured transversely across the relatively small diameter upper portion l04b of the working barrel 104. The central divider block 156 carries an annular sealing element 158 around the bore 154, which sealing element sealingly engages the actuator rod 132 as the actuator rod.

reciprocates through the central divider block. A weight counterbalancing spring 160 is positioned between the upper side of the central divider block 156 and the spider 152 to carry or balance the weight of the slide valve assembly constituted by the lower and upper slide valve members 146 and 148, respec-. tively, and the actuator rod 132.

Mounted on the wall of the relatively small diameter portion 104b of the working barrel 104 at the location which is aligned with the lower slide valve member 146 is a spring and ball assembly 162. The spring and ball assembly 162 is constructed similarly to the spring and ball assemblies 46 and 48 which have been hereinbefore described in referring to the doubleacting embodiment of the invention depicted in FIGS. 1-3. Thus, the spring and ball assembly 162 includes a cap plate 164 which has a recess formed therein to accommodate a spring 166 which biases a ball 168 radially inwardly through an aperture or opening formed in the side of the working barrel. The outer peripheral wall of the lower slide valve member 146 has a semispherical recess 170 formed therein adjacent the ball 168 so that the snap action to which reference has hereinbefore been made can be obtained as the lower slide valve member 146 is shifted.

In similar fashion, a spring and ball assembly 172 is secured to the relatively small diameter portion 104b of the working barrel 104 adjacent the upper slide valve member 148. The spring and ball assembly 172 is constructed identically to the spring and ball assembly 162 and thus includes a cap plate 174 which is recessed to receive a spring 176 which biases a ball 178 inwardly against the wall of the upper slide valve member 148. As illustrated in FIG. 4, the ball 178 is positioned in an accommodating recess 180 formed in the outer peripheral wall of the upper slide valve member 148. As will be hereinafter explained, when the slide valve assembly which includes the upper and lower slide valve members, 148 and 146, respectively, is shifted, the ball 178 will be caused to move out of the recess 180 and onto the adjacent relatively smooth peripheral surface ofthe upper slide valve member.

It will be noted in referring to the upper slide valve member 148 that this slide valve member is ported and thus contains a pair of radial ports 182 and 184. It will also be noted that the radial ports 182 and 184 are located between a series of annular sealing rings, these being designated by reference numerals 186, 188 and 190. The lower slide valve member 146 also is provided with a pair of radial ports 192 and 194 extending through the wall thereof. Located on the opposite sides of the radial ports 192 and 194 are a series of annular sealing rings 196, 198 and 200. The sealing rings 196, 198 and 200 extend around the outer periphery of the lower slide valve member 146 and sealingly engage the internal wall of the small diameter portion l04b of the working barrel 104.

Extending from the upper end portion of the relatively small diameter portion 104b of the working barrel 104 is a first power fluid charging conduit 202. It will be noted that the upper end of the first power fluid charging conduit 202 communicates with the interior of the working barrel 104 through a suitable fitting or port at a location which is immediately below the radial port 182 formed in the upper slide member 148. At its other end, the first power fluid charging conduit 202 communicates with the lower end of the relatively large diameter portion 104a of the working barrel 104 through a suitable port or fitting.

A second power fluid charging conduit 204 is connected at its upper end. to the interior of the working barrel 104 through a suitable port or fitting which, as illustrated in FIG. 4, is aligned in one operative position of the pump with the radial port 184 in the upper slide valve member 148. The lower end of the second power fluid charging conduit 204 is connected through a suitable port or fitting to the upper end of the relatively large diameter portion 104a of the working barrel 104 so that power fluid is charged from the second power fluid charging conduit 204 to a portion of the working barrel 104 which is above the power piston 108.

A power fluid discharge conduit 206 extends from the bottom of the relatively large diameter portion 104a of the working barrel 104 and is communicated with the interior of the working barrel through a suitable port or fitting located opposite the lower slide valve member 146. As illustrated in FIG. 4, in one operative position of the pump, the upper end of the power fluid discharge conduit 206 registers with the radial port 192 formed through the lower slide valve member 146 so that power fluid discharged from the working barrel during one portion of the stroke of the power piston 108 is forced through the conduit 206 and through the radial port 192 to the interior of the hollow sleeve constituting the lower slide valve member 146.

A second power fluid discharge conduit 208 extends from the upper portion of the relatively large diameter portion 104a of the working barrel 104 and is connected at its upper end to the relatively small diameter portion 10417 of the working barrel at a location which is opposite the lower slide valve member 146. At this location, the upper end of the power fluid discharge conduit 208 can be communicated with the hollow interior of the lower slide valve member 146 through the radial port 194 at a time when the slide valve assembly is shifted as hereinafter described. Positioned immediately below the central divider block 156 and above the lower slide valve member 146 is a radial port 210 which opens through the relatively small diameter portion 104k of the working bar rel 104 so as to place the interior of the working barrel in communication with the annulus between the outer tubing I00 and the working barrel 104. This annulus is continuous, and in communication, with an annulus formed between the inner tubing 102 and the outer tubing 100, and this annulus extends all the way to the surface for the purpose of returning power fluid and production fluid to the surface as hereinafter explained.

Secured to the lower end of the pump barrel is a stand ing valve housing 212. The standing valve housing 212 contains a movement limiting spider 214 which limits the upward movement in the standing valve housing of a standing valve ball 216. The standing valve ball 216 is shown seated upon a seat formed at the upper end of a port or orifice 218 which permits the interior of the standing valve housing 212 to communicate with a sandpipe 220 when the standing valve ball 216 is unseated as hereinafter explained.

Operation of the Embodiment of the Invention Depicted in Figure 4 Upon commencement of the operation of the single-acting pump embodiment of the invention depicted in FIG. 4, power fluid is delivered from the surface of the ground down the hole to the pump via the inner tubing 102. The power fluid thus delivered to the pump passes into the interior of the upper slide valve member 148. This fluid, however, cannot pass the central divider block 156 so as to enter the lower portion of the working barrel 104.'The power fluid, in the illustrated status of the pump, passes through the radial port 184 and enters the second power fluid charging conduit 204. From this conduit, power fluid is charged to the upper end of the relatively large diameter portion 104a of the working barrel 104. As the power fluid enters this portion of the working barrel, it forces the power piston 108 downwardly in the relatively large diameter portion 104a of the working barrel 104.

Downward movement of the power piston 108 forces any liquid which may be located therebelow out through the power fluid discharge conduit 206 which, as illustrated, is at this time communicated with the interior of the working barrel through the radial port 192 formed in the lower slide valve member 146. The fluid which is forced through the power fluid discharge conduit 206 will actually be a mixture of power fluid and production fluid, as production fluid has previously been drawn into the lower end of the relatively large diameter portion 104a of the working barrel 104 in a manner hereinafter to be described. As the mixture of power fluid and production fluid passes into the hollow interior of the working barrel 104 through the radial port 192 formed in the lower slide valve member 146, this fluid accumulates above the partition 106, and ultimately will flow through the radial port 210 into the annulus between the working barrel 104 and the outer tubing 100. From this point, the fluid can be forced to the surface by the further downward movement of the power piston 108.

It should be pointed out that the fluid which is forced from the space beneath the power piston 108 by the downward movement of the power piston cannot flow upwardly through the first power fluid charging conduit 202 due to the interruption of the communication of the upper end of this conduit with the interior of the working barrel 104 by the upper slide valve member 148. in other words, at this time during the operation of the pump shown in FIG. 4, the upper slide valve member 148 is in a blocking position which closes the entrance to the first power fluid charging conduit 202 and prevents power fluid from entering this conduit, and likewise prevents any fluid from being forced by the power piston 108 upwardly through this conduit and into the interior of the working barrel 104.

As power piston 108 continues to move downwardly in the relatively large diameter portion 104a of the working barrel 104, the elongated tubular member 114 and the pump piston 116 carried on the lower end thereof are also forced downwardly within the pump barrel 120. If it be assumed that, at this time, production fluid has previously entered the pump barrel 120 via the sandpipe 212, it will be seen that the effect of this downward movement of the elongated tubular member 114 and pump piston 116 is to force the standing valve ball 216 against its seat, and thus close the port 218 and prevent retrograde flow of production fluid out through the sandpipe 212. The traveling valve ball 124, on the other hand, is lifted off its seat l22 and production fluid can flow upwardly into the space beneath the traveling valve ball 124 and out through the radial orifices 130. Thus, production fluid can fill the annular space between the elongated tubular member 114 and the pump barrel 120 during the downstroke of the power piston 108.

As the power piston 108 moves downwardly to approach the lower end of the enlarged diameter portion 104a of the working barrel 104, the power piston strikes the lower collar 136 secured to the lower end of the actuator rod 132 with the result that the actuator rod is forced downwardly. The downward movement of the actuator rod 132 necessarily carries with it in a corresponding downward movement the lower slide valve member 146 and the upper slide valve member 148 which are secured to the actuator rod through the spiders 150 and 152, respectively. The shifting of the lower and upper slide valve members 146 and 148, respectively, in this manner, initiates the throw or stroke of the slide valve assembly. This throw or shifting of the slide valve assembly is then carried through by the snap action which is developed by the ball and spring assembly 162. In other words, as the ball 168 reaches the edge of the semispherical recess 170 formed in the outer periphery of the lower slide valve member 146, the spring 166 biases the ball into this recess, and the slide valve assembly is snapped downwardly to complete its downward shift to the second alternate position which is to effect stroke reversal as hereinafter described. At the same time, the initial contact of the power piston 108 with the collar 136 formed on the lower end of the actuator rod 132 moves the upper slide valve member 148 to a position such that the ball 178 rides on the outer peripheral surface of the upper slide valve member and leaves the recess 180.

As the slide valve assembly is shifted in the manner described, the effect of the shift is to interrupt communication of the interior of the working barrel 104 with the second power fluid charging conduit 204 by moving the radial port 184 downwardly out of registry with the entrance to this conduit. Simultaneously, the radial port 182 in the upper slide valve member 148 is moved downwardly into registration with the opening into the first power fluid charging conduit 202. Thus, at this time, power fluid is able to pass from the upper end of the working barrel 104 into the first power fluid charging conduit 202 and downwardly in this conduit to enter the lower end of the relatively large diameter portion 1040 of the working barrel 104. Power fluid is thus now being delivered to the underside of the power piston 108. Simultaneously with the shifts of the upper slide valve member 148 in the manner described to change the status of the radial ports 182 and 184, the lower slide valve member 146 shifts downwardly so that the radial port 192 moves out of registry with the opening in the upper end of the power fluid discharge conduit 206 and the radial port 194 is moved into registry with the upper end of the power fluid discharge conduit 208.

As power fluid commences to act against the lower side of the power piston 108, the downward movement of the power piston 108 is completely arrested and stroke reversal occurs. The power piston 108 thus commences to move upwardly in the relatively large diameter portion 104a of the working barrel 104. This movement ofthe power piston 108 forces liquid located above the power piston out through the power fluid discharge conduit 208 and through the radial port 194 into the hollow interior of the lower slide valve member 146. This discharge power fluid is then free to flow through the radial port 210 in the working barrel 104 into the annulus between the working barrel and the outer tubing 100. The upward movement of the power piston 108 also creates a reduced pressure in the lower end of the relatively large diameter portion 104a of the working barrel 104 with the result that production fluid which has been moved into the annulus between the pump barrel and the elongated tubular member 114 in the manner hereinbefore described is drawn upwardly into the space beneath the power piston 108 where it is mixed with the incoming power fluid. The upward movement of the production fluid is also caused by the pumping action developed by the pump piston 116. At this time, the traveling valve member 124 is seated on the seat 122 so that retrograde flow of this production fluid cannot occur. At the same time, the upward movement of the pump piston 116 results in additional production fluid being drawn upwardly through the sandpipe 212 and through the port 218 which is then opened by the unseating of the standing valve 216. Production fluid thus moves upwardly through the standing valve housing 212 and fills the lower end of the pump barrel 120.

As the power piston 108 approaches the upper end of the enlarged diameter portion 104a of the working barrel 104, it strikes the upper collar 134 on the actuator rod 132 to commence the upward shifting movement of the slide valve assembly which includes the upper slide vale member 148 and the lower slide valve member 146. This upward shifting of the slide valve assembly is carried through by the snap action effected by the spring and ball assembly 162. Thus, the pump is, at this time, returned to the status depicted in FIG. 4, and the stroke of the pump is completed. It will be noted that, in this embodiment of the invention, both the power fluid and the production fluid produced by the pump are returned to the surface by circulation of the fluid mixture through the radial port 210 and into the annulus between the working barrel 104 and the outer tubing 100.

From the foregoing description of the invention, it will have become apparent that it is an important object of the invention toprovide an improved down hole hydraulic pump which employs a unique slide valve action by which the dual slide valves are positively snapped to one of two alternate positions to effect stroke reversal of the pump.

Although certain preferred embodiments of the invention have been illustrated in the drawings and hereinbefore described, it is to be understood that various changes and modifications of these embodiments can be effected without departure from the basic principles of the invention. Changes and innovations of this type are therefore deemed to be circumscribed by the spirit and scope of the invention.

What 1 claim is:

1. A hydraulic pump comprising:

a working barrel having an upper portion and a lower portion;

an upper power piston disposed in the upper portion of said working barrel;

a lower power piston disposed in the lower portion of said working barrel;

: connecting rod means interconnecting said upper power piston and said lower power piston;

a central divider block extending transversely acros s the central portion of said working barrel and sealingly separating the upper portion of said working barrel from the lower portion of said working barrel, said central divider bloclcsealingly surrounding said connecting rod means, said connecting rod means extending slidingly through said centralidivider block; s

wherein said cam follower device comprises a spring and balLassembly mounted in the wall of said working barrel and cooperating with said cam surface.

. A hydraulic pump comprising:

working barrel having an upper portion and a lower portion; 1 r 7 7 power piston means slidably disposed in the lower portion of said working barrel for reciprocation therein;

ower fluid charging conduit means connected to, and compower fluid charging conduit means connected to, and communicating with, the interior of Said walking barrel at municating with, the interior of said working barrel at two locations Spaced therealong for alternately driving said locations spaced tlierealong for alternately driving said lPower Piiton n t first in one direction in Said working power piston means, first in one direction in said working barrel, in the opposite'idil'ection Said Working barrel, then in the opposite direction in said working bar- 1 5 7 re]? 2 :rel; e 7;; power fluid discharge conduit means connected to, and Tower fl id discharge mm t; connected to and communicating with, the interior ofsaid working barrel at communicating with,the interior of said working barrei'at Y lQcatlon's Spaced l ng, and spaced from sa d two locations spaced therealong, and spaced from said first memlonedrlwoi fii h f r'recciving power fluid first-mentioned two locations for receiving power fluid i m Said 'workmg W at f times discharged from said working barrel at different times ai the reclprocanqn of 531g power plston means 7 7 em; g gg refilprocducn of Sald n t a slide valve assem bly slidably positioned in said working a slide valve assembly slidably positioned in said working barrel and inguding I t a first slide valve positioned over one of said firstg-m ena firstslide valve positioned in said working barrel on one tioned two 9 to ckisc one P of 'f 'f" side of said central divider block over one of said firstof f mteflof 0f 831d t l'klng barrel with said power fluid charging conduit means, said first slide mentioned two locations to close one point of communication of the interior of said working barrel with said valve F movable Second P m power fluid' charging conduit means, said first slide valve '7 9 Pomt of P i of Interior the work.- bin movable to Second n to r; en said one 0i t ing barrel wlth Sald power fluid charging conduit g a z p r p p n 7 means of communication of the interior of the working barrel a e o a second slide valve positioned over one of said secondrrwnh Said Power fluld Chargmg conduit means; mentioned two iocations to close one point of commuarrsrecond snide valve prositionedjein Said wdrking barrel on the nication of the interior of said working barrel with said "opposite'side of said central divider block and over one of power fluid disaharge ccmduit means Sad Second Slide isaid second-mentioned twoiocations'to close one point of vave being movable to a Second position w open Said communication of the interior of said workin barrel with ,7 i 77 said power fluid discharge conduit means, s aid second s, of urelgcauon a EE- 3 of 2 7 slide valve being movable to a second position to open 40 mzf s are Sal Power, W con mt 531d point manor of an actuator rod secured'to said first slide valve and said g gggg barrelJvHh Sam power fluld P m second slide valve and extending axially in said working barrel; and 7 e gf li zf q fig 't secondjnde Valves for Z a earn surface positioned adjacent said working barrel co cum, moveme 1 m erconnec mg means and m vabl with id firs nd econ lide valves nd tending slidingly -E Said ceimal dividr mock; and with the aciuator fod inttei' coniiectiri g said first side a cam surface positioned adjacent said working barrel and valve and Second slide valve; movable with said first and second slide galves and intera fi t collar "Secured around aid aotuator d and osiconnetmg E 1 tioned above said power piston; i meafisfoopemimg Sald Power 'l trarlsferrmg a second collar secured aroundisaid actuator rod and posimotion from said power pistons to said slide valve astioned belew Said power piston; Se?rn bly; a i a spring-biased cam follower device resiliently bearing a f F cam follower? dev'ce gslhntly beanng against said cam surface, and substantially immovable in 5 i car n surface, and substantially lmmovable in earn axial direction in said working barrel, said cam fol- 3X13] directlo" 531d (P bfineli Said Cam lower device cooperating with said cam surface to al- Ower device coogerating with Said cam surface 7, ternately snap said slide valve assembly between two P Said Siide 3 assembly beiween operating positions in saidworking barrel in a reciprocatnoperating positions in said working barrel in a reciprocati movement;

ing movgement' I a partition extending transversely across said working barrel A hydraulic P p as defined in 59 1 3316mm said between said slide valve assembly and said power piston P p incllldes one said Surfaces located a Portion and sealingly separating the portion of the working barrel f each of m Slide Valves; 5 containing said power piston from the portion of said and wherein said P p furEher includes one of Said cam working barrei containing said slide valve assembly, said lower; devices bearing against each of said cam surfaces, it partition slidingiy receiving, Said actuator rod each of said cam follower devicegcomprising: therethrough; d a rolling mereber contacting the respective cam surface a divider block positioned between said first slide valve and and at least Partially seated p in the Wall Of said second slide valve and extending sealingly across said Said ng 5 working barrel, and slidingly receiving said actuator rod a spring mounted on the wall of the working barrel and h h h I e biasing the rolling member against the cam surface. 5,

3. A hydraulic pump as definet? in claim 1 wherein said pump further includes a cam block mountedgon said interconnecting means and carrying said cam surface; and: z

A hydraulic pump comprising:

a working barrel having an upper portion and a lower portion; 3

an :upper power piston slidably positioned in the upper portion of said working barrel for reciprocation therein;

a lower power piston slidably disposed in the lower portion of said working barrel for reciprocation therein;

connecting rod means interconnecting said upper power piston and said lower power piston;

power fluid charging conduit means connected to, and communicating with, the interior of said working barrel at two locations spaced therealong for alternately driving said power pistons, first in one direction in said working barrel, then in the opposite direction in said working barrel;

power fluid discharge conduit means connected to, and communicating with, the interior of said working barrel at two locations spaced therealong, and spaced from said first-mentioned two locations for receiving power at different times during the reciprocation of said power pistons therein;

a slide valve assembly slidably positioned in said working barrel in axial alignment with said power pistons and including a first slide valve positioned in said working barrel in axial alignment with said power pistons and over one of said first-mentioned two locations to close one point of communication of the interior of said working barrel with said power fluid charging conduit means, said first slide valvebeing movable axially in said working barrel to a second position to open said one point of communication of the interior of the working barrel with said power fluid charging conduit means;

a second slide valve positioned in said working barrel in axial alignment with said power pistons and over one of said second-mentioned two locations to close one point of communication of the interior of said working barrel with said power fluid discharge conduit means, said second slide valve being movable to a second position to open said one point of communication of the interior of said working barrel with said power fluid discharge conduit means;

means extending axially in said working barrel and interconnecting said first and second slide valves for concurrent axial r'novement in said working barrel; and

a cam surface positioned adjacent said working barrel and movable with said first and second slide valves and interconnecting means;

means cooperating with said power piston means for transferringmotion from said power piston means to said slide valve assembly;

a spring-biased cm follower device resiliently bearing against said cam surface, and substantially immovable in an axial direction in said working barrel, said cam follower device cooperating with said cam surface toalternately snap said slide valve assembly between two operating positions in said working barrel in a reciprocating movement;

a standing valve housing secured to the lower end of said working barrel;

a standing valve in said standing valve housing;

means for conveying fluid from a fluid-producing formation around said pump to said standing valve housing;

conduit means connected to said working barrel below said lower power piston for receiving production fluid from.

said working barrel;

a second standing valve housing secured to the upper end of said working barrel;

a second standing valve in said second standing valve housing;

second conduit means connected to said second standing valve housing for receiving production fluid discharged through said second standing valve housing from said working barrel; and

third conduit means connected to said working barrel above said upper power piston for conveying fluid from a fluidproducing formation around said pump to the upper portion of said working barrel.

6. A hydraulic pump comprising:

a working barrel having an upper portion and a lower portion; a power piston disposed in the lower portion of said working barrel; power fluid charging conduit means connected to, and communicating with, the interior'of said working barrel at two locations spaced therealong for alternately driving said power piston, first in one direction in said working barrel, then in the opposite direction in said working barrel; power fluid discharge conduit means connected to, and communicating with, the interior of said working barrel at two locations spaced therealong, and spaced from said first-mentioned two locations for receiving power fluid discharged from said working barrel at different times during the reciprocation of said power piston therein; a slide valve assembly slidably positioned in said working barrel and including a first slide valve positioned over one of said first-mentioned two locations to close one point of communication of the interior of said working barrel with said power fluid charging conduit means, said first slide valve being movable to a second position to open said one point of communication of the interior of the working barrel with said power fluid charging conduit means; I a second slide valve positioned over one of said secondmentioned two locations to close one point of communication of the interior of said working barrel with said power fluid discharge conduit means, said second slide valve being movable to a second position to open said one point of communication of the interior of said working barrel with said power fluid discharge conduit means; means interconnecting said first and second slide valves for concurrent movement; and a cam surface positioned adjacent said working barrel and movable with said first and second slide valvesand interconnecting means; means cooperating with said power piston for transferring motion from said power piston to said slide valve assembly;

a spring-biased cam follower device resiliently bearing against said cam surface and substantially immovable in an axial direction in said working barrel, said cam follower device cooperating with said cam surface to alternately snap said slide valve assembly between two operating positions in said working barrel in a reciprocating movement;

a partition extending transversely across said working barrel between said slide valve assembly and said power piston and sealingly separating the portion of the working barrel containing said power piston from the portion of said working barrel containing said slide valve assembly;

a divider block positioned between said first slide valve and said second slide valve and extending sealingly across said working barrel;

a pump barrel connected to the lower end of said working barrel;

a pump piston slidably and reciprocably mounted in said pump barrel;

means connecting said pump piston to said power piston for movement therewith; and

traveling valve means in said pump piston for passing fluid from below to above said pump piston during the downward stroke thereof.

7. A hydraulic pump as defined in claim 6 wherein said power fluid charging conduit means comprises:

a first charging conduit connected at one end to the upper portion of said working barrel at a location aligned with said first slide valve, and connected at a second end to the lower portion of said working barrel at a location above said power piston; and

a second charging conduit connected at one end to the upper portion of said working barrel at a location aligned with said first slide valve, and connected at a second end to the lower portion of said working barrel at a location below said power piston.

8. A hydraulic pump as defined in claim 7 wherein said power fluid discharge conduit means comprises:

a first discharge conduit having one end connected to the lower portion of said working barrel below said power piston, and having a second end connected to the upper portion of said working barrel at a location aligned with said second slide valve; and

a second discharge conduit having one end connected to the lower portion of said working barrel above said power piston, and having a second end connected to the upper portion of said working barrel at a location aligned with said second slide valve.

9. A hydraulic pump as defined in claim 8 and further characterized to include fluid passageway means for conveying fluid from a location within said working barrel above said partition to the surface.

10. A hydraulic pump as defined in claim 9 wherein said cam surface is formed on at least one of said slide valves.

11. A hydraulic pump as defined in claim 10 wherein said interconnecting means comprises an actuator rod secured to said first slide valve and said second slide valve and extending axially in said working barrel and slidingly through said divider block, partition and power piston; and

wherein said means cooperating with said power piston means comprises:

a first collar secured around said actuator rod and positioned about said power piston; and

a second collar secured around said actuator rod and positioned below saidvpower piston.

12. A hydraulic pump as defined in claim 11 wherein said fluid passageway means comprises:

annulus-defining tubular means surrounding said working barrel; and

a port through said working barrel between said slide valves communicating with the annulus between said working barrel and tubular means.

13. A hydraulic pump comprising:

a working barrel having an upper portion and a lower portion;

a power piston slidably positioned in the lower portion of said working barrel for reciprocation therein;

power fluid charging conduit means connected to, and communicating with, the interior of said working barrel at two locations spaced therealong for alternately driving said power piston, first in one direction in said working barrel,

then in the opposite direction in said working barrel;

power fluid discharge conduit means connected to, and

communicating with, the interior of said working barrel at two locations spaced therealong, and spaced from said first-mentioned two locations for receiving power fluid discharged from said working barrel at different times during the reciprocation of said power piston means therein;

a slide valve assembly positioned in said working barrel in axial alignment with said power piston and slidably movable in said working barrel, said slide valve assembly including a first slide valve positioned in said working barrel in axial alignment with said power piston and over one of said first-mentioned two locations to close one point of communication of the interior of said working barrel with said power fluid charging conduit means, said first slide valve being movable to a second position to open said one point of communication of the interior of the working barrel with said power fluid charging conduit means;

a second slide valve positioned over one of said secondmentioned two locations to close one point of communication of the interior of said working barrel with said power fluid discharge conduit means, said second slide valve being movable to a second position to open said one point of communication of the interior of said working barrel with said power fluid discharge conduit means;

an actuator rod interconnecting said first and second slide valves and extending axially in said working barrel, said actuator rod being secured to said first and second slide valves;

a cam surface positioned adjacent said working barrel and movable with said first and second slide valves, and with said actuator rod;

a divider block positioned between said first slide valve and said second slide valve and extending transversely and sealingly across said working barrel;

means cooperating with said power piston for transferring motion from said power piston to said slide valve assembly; and

a spring-biased cam follower device resiliently bearing against said cam surface, and substantially immovable in an axial direction in said working barrel, said cam follower device cooperating with said cam surface to alternately snap said slide valve assembly between two operating positions in said working barrel in a reciprocating movement. 

1. A hydraulic pump comprising: a working barrel having an upper portion and a lower portion; an upper power piston disposed in the upper portion of said working barrel; a lower power piston disposed in the lower portion of said working barrel; connecting rod means interconnecting said upper power piston and said lower power piston; a central divider block extending transversely across the central portion of said working barrel and sealingly separating the upper portion of said working barrel from the lower portion of said working barrel, said central divider block sealingly surrounding said connecting rod means, said connecting rod means extending slidingly through said central divider block; power fluid charging conduit means connected to, and communicating with, the interior of said working barrel at two locations spaced therealong for alternately driving said power piston means, first in one direction in said working barrel, then in the opposite direction in said working barrel; power fluid discharge conduit means connected to, and communicating with, the interior of said working barrel at two locations spaced therealong, and spaced from said firstmentioned two locations for receiving power fluid discharged from said working barrel at different times during the reciprocation of said power piston means therein; a slide valve assembly slidably positioned in said working barrel and including a first slide valve positioned in said working barrel on one side of said central divider block over one of said firstmentioned two locations to close one point of communication of the interior of said working barrel with said power fluid charging conduit means, said first slide valve being movable to a second position to open said one point of communication of the interior of the working barrel with said power fluid charging conduit means; a second slide valve positioned in said working barrel on the opposite side of said central divider block and over one of said second-mentioned two locations to close one point of communication of the interior of said working barrel with said power fluid discharge conduit means, said second slide valve being movable to a second position to open said one point of communication of the interior of said working barrel with said power fluid discharge conduit means; means interconnecting said first and second slide valves for concurrent movement, said interconnecting means extending slidingly through said central divider block; and a cam surface positioned adjacent said working barrel and movable with said first and second slide valves and interconnecting means; means cooperating with said power pistons for transferring motion from said power pistons to said slide valve assembly; and a spring-biased cam follower device resiliently bearing against said cam surface, and substantially immovable in an axial direction in said working barrel, said cam follower device cooperating with said cam surface to alternately snap said slide valve assembly between two operating positions in said working barrel in a reciprocating movement.
 2. A hydraulic pump as defined in claim 1 wherein said pump includes one of said cam surfaces located on a portion of each of said slide valves; and wherein said pump further includes one of said cam follower devices bearing against each of said cam surfaces, each of said cam follower devices comprising: a rolling member contacting the respective cam surface and at least partially seated in an opening in the wall of said working barrel; and a spring mounted on the wall of the working barrel and biasing the rolling member against the cam surface.
 3. A hydraulic pump as defined in claim 1 wherein said pump further includes a cam block mounted on said interconnecting means and carrying said cam surface; and wherein said cam follower device comprises a spring and ball assembly mounted in the wall of said working barrel and cooperating with said cam surface.
 4. A hydraulic pump comprising: a working barrel having an upper portion and a lower portion; a power piston means slidably disposed in the lower portion of said working barrel for reciprocation therein; power fluid charging conduit means connected to, and communicating with, the interior of said working barreL at two locations spaced therealong for alternately driving said power piston means, first in one direction in said working barrel, then in the opposite direction in said working barrel; power fluid discharge conduit means connected to, and communicating with, the interior of said working barrel at two locations spaced therealong, and spaced from said first mentioned two locations for receiving power fluid discharged from said working barrel at different times during the reciprocation of said power piston means therein; a slide valve assembly slidably positioned in said working barrel and including a first slide valve positioned over one of said first-mentioned two locations to close one point of communication of the interior of said working barrel with said power fluid charging conduit means, said first slide valve being movable to a second position to open said one point of communication of the interior of the working barrel with said power fluid charging conduit means; a second slide valve positioned over one of said second-mentioned two locations to close one point of communication of the interior of said working barrel with said power fluid discharge conduit means, sad second slide valve being movable to a second position to open said one point of communication of the interior of said working barrel with said power fluid discharge conduit means; an actuator rod secured to said first slide valve and said second slide valve and extending axially in said working barrel; and a cam surface positioned adjacent said working barrel and movable with said first and second slide valves and with the actuator rod interconnecting said first slide valve and second slide valve; a first collar secured around said actuator rod and positioned above said power piston; a second collar secured around said actuator rod and positioned below said power piston; a spring-biased cam follower device resiliently bearing against said cam surface, and substantially immovable in an axial direction in said working barrel, said cam follower device cooperating with said cam surface to alternately snap said slide valve assembly between two operating positions in said working barrel in a reciprocating movement; a partition extending transversely across said working barrel between said slide valve assembly and said power piston and sealingly separating the portion of the working barrel containing said power piston from the portion of said working barrel containing said slide valve assembly, said partition slidingly receiving said actuator rod therethrough; and a divider block positioned between said first slide valve and said second slide valve and extending sealingly across said working barrel, and slidingly receiving said actuator rod therethrough.
 5. A hydraulic pump comprising: a working barrel having an upper portion and a lower portion; an upper power piston slidably positioned in the upper portion of said working barrel for reciprocation therein; a lower power piston slidably disposed in the lower portion of said working barrel for reciprocation therein; connecting rod means interconnecting said upper power piston and said lower power piston; power fluid charging conduit means connected to, and communicating with, the interior of said working barrel at two locations spaced therealong for alternately driving said power pistons, first in one direction in said working barrel, then in the opposite direction in said working barrel; power fluid discharge conduit means connected to, and communicating with, the interior of said working barrel at two locations spaced therealong, and spaced from said first-mentioned two locations for receiving power at different times during the reciprocation of said power pistons therein; a slide valve assembly slidably positioned in said working barrel in axial alignment with said power pistons and including a first slide valve positioned in said working barrel in axial alignmenT with said power pistons and over one of said first-mentioned two locations to close one point of communication of the interior of said working barrel with said power fluid charging conduit means, said first slide valve being movable axially in said working barrel to a second position to open said one point of communication of the interior of the working barrel with said power fluid charging conduit means; a second slide valve positioned in said working barrel in axial alignment with said power pistons and over one of said second-mentioned two locations to close one point of communication of the interior of said working barrel with said power fluid discharge conduit means, said second slide valve being movable to a second position to open said one point of communication of the interior of said working barrel with said power fluid discharge conduit means; means extending axially in said working barrel and interconnecting said first and second slide valves for concurrent axial movement in said working barrel; and a cam surface positioned adjacent said working barrel and movable with said first and second slide valves and interconnecting means; means cooperating with said power piston means for transferring motion from said power piston means to said slide valve assembly; a spring-biased cm follower device resiliently bearing against said cam surface, and substantially immovable in an axial direction in said working barrel, said cam follower device cooperating with said cam surface to alternately snap said slide valve assembly between two operating positions in said working barrel in a reciprocating movement; a standing valve housing secured to the lower end of said working barrel; a standing valve in said standing valve housing; means for conveying fluid from a fluid-producing formation around said pump to said standing valve housing; conduit means connected to said working barrel below said lower power piston for receiving production fluid from said working barrel; a second standing valve housing secured to the upper end of said working barrel; a second standing valve in said second standing valve housing; second conduit means connected to said second standing valve housing for receiving production fluid discharged through said second standing valve housing from said working barrel; and third conduit means connected to said working barrel above said upper power piston for conveying fluid from a fluid-producing formation around said pump to the upper portion of said working barrel.
 6. A hydraulic pump comprising: a working barrel having an upper portion and a lower portion; a power piston disposed in the lower portion of said working barrel; power fluid charging conduit means connected to, and communicating with, the interior of said working barrel at two locations spaced therealong for alternately driving said power piston, first in one direction in said working barrel, then in the opposite direction in said working barrel; power fluid discharge conduit means connected to, and communicating with, the interior of said working barrel at two locations spaced therealong, and spaced from said first-mentioned two locations for receiving power fluid discharged from said working barrel at different times during the reciprocation of said power piston therein; a slide valve assembly slidably positioned in said working barrel and including a first slide valve positioned over one of said first-mentioned two locations to close one point of communication of the interior of said working barrel with said power fluid charging conduit means, said first slide valve being movable to a second position to open said one point of communication of the interior of the working barrel with said power fluid charging conduit means; a second slide valve positioned over one of said second-mentioned two locations to close one point of communication of the interior of said working barrel with said power fluid discHarge conduit means, said second slide valve being movable to a second position to open said one point of communication of the interior of said working barrel with said power fluid discharge conduit means; means interconnecting said first and second slide valves for concurrent movement; and a cam surface positioned adjacent said working barrel and movable with said first and second slide valves and interconnecting means; means cooperating with said power piston for transferring motion from said power piston to said slide valve assembly; a spring-biased cam follower device resiliently bearing against said cam surface and substantially immovable in an axial direction in said working barrel, said cam follower device cooperating with said cam surface to alternately snap said slide valve assembly between two operating positions in said working barrel in a reciprocating movement; a partition extending transversely across said working barrel between said slide valve assembly and said power piston and sealingly separating the portion of the working barrel containing said power piston from the portion of said working barrel containing said slide valve assembly; a divider block positioned between said first slide valve and said second slide valve and extending sealingly across said working barrel; a pump barrel connected to the lower end of said working barrel; a pump piston slidably and reciprocably mounted in said pump barrel; means connecting said pump piston to said power piston for movement therewith; and traveling valve means in said pump piston for passing fluid from below to above said pump piston during the downward stroke thereof.
 7. A hydraulic pump as defined in claim 6 wherein said power fluid charging conduit means comprises: a first charging conduit connected at one end to the upper portion of said working barrel at a location aligned with said first slide valve, and connected at a second end to the lower portion of said working barrel at a location above said power piston; and a second charging conduit connected at one end to the upper portion of said working barrel at a location aligned with said first slide valve, and connected at a second end to the lower portion of said working barrel at a location below said power piston.
 8. A hydraulic pump as defined in claim 7 wherein said power fluid discharge conduit means comprises: a first discharge conduit having one end connected to the lower portion of said working barrel below said power piston, and having a second end connected to the upper portion of said working barrel at a location aligned with said second slide valve; and a second discharge conduit having one end connected to the lower portion of said working barrel above said power piston, and having a second end connected to the upper portion of said working barrel at a location aligned with said second slide valve.
 9. A hydraulic pump as defined in claim 8 and further characterized to include fluid passageway means for conveying fluid from a location within said working barrel above said partition to the surface.
 10. A hydraulic pump as defined in claim 9 wherein said cam surface is formed on at least one of said slide valves.
 11. A hydraulic pump as defined in claim 10 wherein said interconnecting means comprises an actuator rod secured to said first slide valve and said second slide valve and extending axially in said working barrel and slidingly through said divider block, partition and power piston; and wherein said means cooperating with said power piston means comprises: a first collar secured around said actuator rod and positioned about said power piston; and a second collar secured around said actuator rod and positioned below said power piston.
 12. A hydraulic pump as defined in claim 11 wherein said fluid passageway means comprises: annulus-defining tubular means surrounding said working barrel; and a port through said working barrel between said Slide valves communicating with the annulus between said working barrel and tubular means.
 13. A hydraulic pump comprising: a working barrel having an upper portion and a lower portion; a power piston slidably positioned in the lower portion of said working barrel for reciprocation therein; power fluid charging conduit means connected to, and communicating with, the interior of said working barrel at two locations spaced therealong for alternately driving said power piston, first in one direction in said working barrel, then in the opposite direction in said working barrel; power fluid discharge conduit means connected to, and communicating with, the interior of said working barrel at two locations spaced therealong, and spaced from said first-mentioned two locations for receiving power fluid discharged from said working barrel at different times during the reciprocation of said power piston means therein; a slide valve assembly positioned in said working barrel in axial alignment with said power piston and slidably movable in said working barrel, said slide valve assembly including a first slide valve positioned in said working barrel in axial alignment with said power piston and over one of said first-mentioned two locations to close one point of communication of the interior of said working barrel with said power fluid charging conduit means, said first slide valve being movable to a second position to open said one point of communication of the interior of the working barrel with said power fluid charging conduit means; a second slide valve positioned over one of said second-mentioned two locations to close one point of communication of the interior of said working barrel with said power fluid discharge conduit means, said second slide valve being movable to a second position to open said one point of communication of the interior of said working barrel with said power fluid discharge conduit means; an actuator rod interconnecting said first and second slide valves and extending axially in said working barrel, said actuator rod being secured to said first and second slide valves; a cam surface positioned adjacent said working barrel and movable with said first and second slide valves, and with said actuator rod; a divider block positioned between said first slide valve and said second slide valve and extending transversely and sealingly across said working barrel; means cooperating with said power piston for transferring motion from said power piston to said slide valve assembly; and a spring-biased cam follower device resiliently bearing against said cam surface, and substantially immovable in an axial direction in said working barrel, said cam follower device cooperating with said cam surface to alternately snap said slide valve assembly between two operating positions in said working barrel in a reciprocating movement. 